Session Initiation Protocol (SIP) is a communication signaling format that applications use to set-up communication sessions. Many of these communication sessions transfer live audio and/or video, files, and messages between computers, smartphones, and the like. In some cases, wireless communication devices use SIP to establish emergency communication sessions with the appropriate emergency responders.
SIP messages have multiple headers to convey various pieces of information, such as message type, user addressing, call-IDs, hop counts, and the like. One of these headers is the P-Access-Network-Info (P-Net-Info) header that provides information about the access network used by the wireless communication device. In wireless access networks, a SIP-based communication device may indicate its serving base station and access technology in the P-Net-Info header. SIP-based communication devices on the session may use this access network information to optimize the media for the specified wireless access technology.
In some cases, the P-Net-Info header includes a Base Station Identifier (BSID) that represents a course location for the user. The course location can be used to provide location-based services to the user—including emergency services. The location information in the P-Net-Info header may be private, and access networks typically remove the P-Net-Info header from SIP messages before their transfer outside of the network.
On an emergency call from a wireless communication device, the device transfers a SIP INVITE message having a “priority” header with an “emergency” value and a P-Net-Info header with the serving BSID. This emergency INVITE message is received and processed by a complex of Call State Control Functions (CSCFs) in an Internet Protocol (IP) Multimedia core network Subsystem (IMS). A Proxy-CSCF (P-CSCF) will process the emergency INVITE message, and based on the emergency service indicator, the priority header, and other information, the P-CSCF forwards the INVITE message to an Emergency-CSCF (E-CSCF).
The E-CSCF invokes a Location Routing Function (LRF) to verify the BSID in the P-Net-Info header. The LRF communicates with the wireless access network to verify which BSID is currently serving the wireless communication device. If the network-provided BSID differs from the user-provided BSID, then the E-CSCF uses the network-provided BSID for routing since it is typically more accurate due to user device malfunctions, user hacking, and the like. The E-CSCF selects the route for the emergency call based on the network-provided BSID in these scenarios.
In another emergency call example, a wireless communication device transfers a SIP INVITE message having a “priority” header with an “emergency” value, but the INVITE does not have a P-Net-Info header. The emergency INVITE message is processed by P-CSCF which forwards the emergency INVITE message to the E-CSCF. The E-CSCF invokes the Location Routing Function (LRF) to obtain a serving BSID for the wireless communication device. The E-CSCF then selects a route for the emergency call based on the network-provided BSID.
Session Description Protocol (SDP) is used to exchange session information between endpoints in a SIP session. The SDP file with the session data is typically carried in the payloads of the SIP messages. In some cases, a wireless communication device will indicate its current GPS coordinate location in the SDP file carried in a SIP payload. This GPS location may be used by the systems on the session to provide location-based services.
Unfortunately, the use of location data in SIP and SDP messages is inefficient and lacks effective user controls.